Midlatitude ionospheric plasma temperature climatology and empirical model based on Saint Santin incoherent scatter radar data from 1966 to 1987

Abstract

[1] Ionospheric plasma temperature variations have recently been studied based on incoherent scatter radar (ISR) observations at a lower midlatitude site, Shigaraki, in East Asia ] and Millstone Hill, a typical subauroral midlatitude site in North America [Zhang and Holt, 2004]. The French Saint Santin ISR, with a geographic latitude slightly higher but an apex latitude 14°lower than Millstone, collected bistatic and quadristatic measurements for over two solar cycles beginning in September 1965. A database of these data, containing observations between 1966 and 1987, has been used in this study in order to establish the midlatitude ionospheric climatology, in particular that of the upper atmosphere thermal status, as well as empirical models for space weather applications. This paper presents, in comparison with the Millstone Hill results, variations of ion and electron temperatures (Ti and Te) with solar activity, season, time of the day, and altitude. The F2 region Te at St. Santin is found to be lower than at Millstone between March and July, when the St. Santin electron density Ne is relatively higher. The midday Te below 300 km increases with F10.7, as at Millstone Hill. Above 300 km it tends to decrease with F10.7 at St. Santin, while it increases in summer at Millstone Hill. Ti between 250 and 350 km peaks midway between spring and summer. We have also created St. Santin ionospheric models for Ne, Te, and Ti using a bin-fit technique similar to that used for the Millstone Hill models. Comparisons with corresponding IRI predications indicate good agreement in Ti at high solar activity, and above the F2 peak, Te from the IRI tends to be higher than both the St. Santin and Millstone Hill models.

The ionospheric behavior in conjugate hemispheres during the 3 October 2005 solar eclipse

“…That is, at higher altitudes (above ∼300 km), the photoelectron heat not only comes from local hemisphere but also from the conjugate hemisphere. Some studies have shown presunrise plasma temperature enhancements was contributed to by the photoelectron heating from the conjugate sunlit region (Evans, 1973;Peterson et al, 1977;Chao et al, 2003, Zhang et al, 2004. During a solar eclipse, photoelectrons in the eclipse region are reduced largely at totality, then in its conjugate region the inflow photoelectron flux from the eclipse region will decrease a lot, which results in a large decrease in electron temperature in this region.…”

The ionospheric responses to the 11 August 1999 solar eclipse: observations and modeling

“…The phenomenon of the energetic photoelectron flow from a conjugate sunlit hemisphere to a darkness hemisphere has been mentioned and considered in some papers in the past (e.g. Evans, 1973;Schunk and Nagy, 1978;Bailey and Sellek, 1990;Chao et al, 2003, Zhang et al, 2004Lei et al, 2007;Bilitza et al, 2007). When the Northern Hemisphere is in darkness during the eclipse, the magnetic conjugate-points in the Southern Hemisphere are still illuminated.…”

Ionospheric response to total solar eclipse of 22 July 2009 in different Indian regions

“…As a result photoionization activity in the ionosphere during the eclipse period decreases to almost nighttime conditions. The changes in the electron density distribution and the total electron content (TEC) have been studied using different techniques such as the Faraday rotation measurements (Tyagi et al, 1980;DasGupta et al, 1981), ionosonde networks (Venkatesh et al, 2011), incoherent scatter radars (Zhang et al, 2004), GPS systems (Ramarao et al, 2006) and satellite measurements (Davies and Hartmann, 1997). GPS systems provide data with better accuracy both in time and space and hence are widely used in ground-based studies (Bagiya et al, 2011;Kumar and Singh, 2011;Galav et al, 2011).…”